[DOCS] Enhancements to Users page

[jmikell821]

Topic to update: https://www.elastic.co/guide/en/security/current/users-page.html

Related issue: elastic/kibana#129046
Related PRs:

• [Security Solutions] Add risk tab to the user details page kibana#130256
• [Security Solutions] User risk - Add links to documentation and dashboards kibana#131715

Users by Risk tab

Add the "Users by Risk" tab to the user details page. The tab should be similar to the one on the host details page.
The tab is only visible when riskyUsersEnabled is enabled.

Add Authentication tab

Related issue: elastic/kibana#129047, PR: elastic/kibana#129456

How to test it

1. Enable feature flag riskyUsersEnabled
2. Insert and enable user risk transforms https://github.com/elastic/mechagodzilla/pull/188/files (currently not working)
3. Go to the user page and click on the 'users by risk' tab
4. Click on a user name
5. Click on the 'users by risk' tab
6. Make sure the time range includes dates with user risk data

[SourinPaul]

@jmikell821 connecting our offline conversations here - @randomuserid is working on the URS readme and can share the work-in-progress PR here, so you can review it in parallel. Thanks for collaborating.

[randomuserid]

Have written detailed docs on user risk score, PR is here: elastic/detection-rules#2055